Lapping tape for insulating electrical machinery

ABSTRACT

The present invention relates to a lapping tape for insulating electrical machinery by impregnation comprising a porous substrate material, mica paper, and an adhesive, characterized in that the combined adhesive and curing accelerator for the subsequently added impregnating resin is an oxyamino resin having the formula:   IS USED IN WHICH R1 and R2 each denotes a straight-chain alkyl group having up to four carbon atoms or together denote a lower alkylene group which can be interrupted by a heteroatom, the oxyamino resin being prepared by quantitative reaction of an epoxy resin having a melting point above 50* C (to ASTM E 28) and having at least two ethylene oxide groups per molecule with a secondary amine having the formula:   IN WHICH R1 and R2 have the meaning just given.

United States Patent [191 Mosimann et al.

[ LAPPING TAPE FOR INSULATING Y ELECTRICAL MACHINERY [75] Inventors: Hans Mosirnann, Breitenbach; Peter Heim, Basel; Walter Lutz, Laufen, all of Switzerland [73] Assignee: Schweizerische lsola-Werke,

Breitenbach, Switzerland [22] Filed: .Apr. 7, 1972 [21] Appl. No.: 242,229

[30} ForeignflApplication Priority Data Apr. 8, 1971 Switzerland 5170/71 [52] US. Cl 161/93, 156/331, 161/163, 174/110 R, 260/89.7 N

[51] Int. Cl B321) 19/02, B321) 19/06 [58] Field Of Search 161/93, 163, 88; 174/25,

EP, 47 R, 47 CZ, 89.7 R, 89.7 N, 2 EC, 571, 1

[56] References Cited UNITED STATES PATENTS 3,556,925 l/l971 Mertens 161/163 3,592,711 7/1971 Senarclens..... 161/163 3,695,984 10/1972. Rogers. 161/93 Primary Examiner-Marion E. McCamish Attorney, Agent, or Firm-Wenderoth, Lind & Ponack [451 Apr. 30, 1974 [57] ABSTRACT The present invention relates to a lapping tape for insulating electrical machinery by impregnation comprising a porous substrate material, mica paper, and an adhesive, characterized in that the combined adhesive and curing accelerator for the subsequently added impregnating resin is an oxyamino resin having the formula:

/R1 cream-N H R2 (I) NH I in which R and R have the meaning just given.

6 Claims, No Drawings LAPPING TAPE FOR INSULATING ELECTRICAL MACHINERY The conductors of medium and high voltage and power electric motors and generators are insulated by mica products. In high-voltage windings, the conductor is'insul ated before being placed in its slot, the insulating being in the form of a mica product either in foil form or in the form of a lapping. The total impregnation process .is used at present for windings required to operate at up to about 6 kV i.e., the complete winding is insulated with porous mica strips, and after it has been placed in the slot the finished winding is impregnated with a solvent-free impregnating resin.

In both cases i.e., high-voltage conductors which are fully insulated first, then placed in the slot, and high-voltage conductors treated by being fully impregnated once the winding is in the slot the mica insulation must be completely impregnated .with a solventfree synthetic resin.

If the resin is introduced into awinding by impregnation after the tape has been wound on a conductor bar built up from insulated separate conductors and stuck together, the mica insulation must, if .the process is to be satisfactory, be completely impregnated with the resin in a vacuum pressure process, and so the lapping tape used must be. porous if it is to .be able to take up the resin, particularly in the case of layers having a thickness of several millimeters. Lapping tapes comprise a substrate, e.g. a glass silk fabric having adensity of approximately 25 glm or a mattof glass-orsynthetic fibres, and Mayer of mica. The .purposeof'the substrate is to provide the composite materialwiththe necessary mechanical strengthhTo enable the material to be handled, however, the substrate and the mica must be stuck together by an adhesive. For thisprocedure tobe satisfactory, the starting materials must meet the following requirements.

' The tapemust be mechanically strong and able to withstand mechanical lapping, yet it must be substantially adhesive free so that the-resincan impregnate the lapping thoroughly. Clearly, these two requirements are contradictory, for the mechanical strength of a lapping 'tape is greatr in proportion as the bond provided between the substrateand the mica by a flexibleadhesive is greater, yet'the adhesive is'a hindrance to subsequent impregnation. Endeavorsrare thereforernade for the sticking of the substrate to themica to be as faras possible on a spot basis.

Of course, the adhesive used .for lapping tapes which,

because of the poor tensile strength of the mica paper, are a composite product consisting of mica paper and a high tensile heat-resistantfabric (glass fabric or synthetic fibres) must meetzthe following requirements:

.I a very small quantity-of binder must stickthe mica paper to the substrate satisfactorily-enough for mechanical lapping; I

2. although sticking must be satisfactory, the adhe' sive must penetrate the mica paper to a very reduced extent and must serve substantially or entirely to stick the mica paper to thesubstrate (for the sake of proper impregnation subsequently); and

- 3. the adhesive mustbe compatible with the impregnating resin which will-be used subsequently.

the group of conductors after curing to form a compact inclusion-free insulation.

The impregnating resin must meet a number of requirements:

l. the resin must wet the mica insulation satisfactorily: 2. the viscosity must be low and, if at all possible, be less than 300 cP at the impregnating temperature;

3. if the resin is to be kept in a tank with very little alteration, its viscosity must remain constant in time despite frequent heating in operations to from 50 to C;

4. viscosity must rise very rapidly'in curing, to reduce resin'droppings, and curing must be a rapid operation to ensure a short dwell in the furnace; and

5. the resin must be sufficiently heat-resistant for the lapping to be used at the usual operating temperatures (class F, 155 C). The resin must therefore not soften appreciably at such temperature and it must lose little, if any, weight at this temperature in continuous operation.

High voltage insulation is required to have low dielectric losses i.e., its .tg must rise very little with voltage and temperature. The insulation must not soften below peak operating temperatures. These two requirements make it impossible to use resins diluted withlarge quantities of a reactive diluent. Reactive diluents are monofunctional low-viscosity epoxy compounds which, because of their monofunctional feature, act as chain stoppers and thus inhibit the formation of long polymer chains. After curing, therefore, the Marten point (to DIN 53 462) or the-dimensional stability (to ISO R shifts to lower temperatures as compared with a diluent-free mixture. If the diluted resinsalready discussed are excluded, few appropriate impregnated-resin systems having viscosities below 1,000 c? at 20 C are left.

Since a low-viscosity resin penetrates the winding more readily than a high-viscosity resin, endeavors are made to increase the temperature. The impregnating resin therefore starts to react so that viscosity increases; unless the throughput is large so that fresh resin can always be added, the mixture soon becomes unserviceable for the proposed purpose. It would therefore be desirable to have a resin system which reacts very little at the temperature of impregnation and example of such a system would be an epoxyresinand a liquid anhydride. Unfortunately, such systems drip for a long time, since they react slowly even at elevated temperature.

The suggestion was therefore made to addan accelerator to the lapping tape. As conventional kinds of accelerator for systems of this kind there can be considered metal naphth-enates and octoates, e.g. cobalt or zinc naphthenate or octoate, tertiary amines, such as e.g. benzyldimethylamine, dimethylaminomethylphenol 2, 4, 6-tri (dimethylaminoethyl) phenol or tri (methoxycarbonylethyl) amine, and boron fluorideamine complexes, e.g. boron fluoride ethylamine or piperidine or pyridine. For instance, German Auslegeschrifts Pat. Nos. 1,162,898 and 1,219,554 disclose a 6 The impregnating resin, .besideshaving all the required insulating properties, must have a low enough viscosity to 'enter'the porous insulation and stick it to process for dipping the rolls of tape before lapping into accelerator solution and drying them. After lapping, the impregnating resin in the tape contacts theaccelerator and it is considered thatreaction acceleration occurs substantially locallyin the lapping; Since the substances concerned are low-molecular substances, some of them are dissolved out of the impregnating resin and therefore reach the resin supply. Consequently, the acceleration acts in the supply too, more particularly because the resin is at a temperature of from about 50 to 60 C during impregnation.

Surprisingly, an adhesive for sticking mica paper to substrate has been found which meets all requirements I very satisfactorily and also acts catalytically on the stable resin curing agent systems mentioned. The novel adhesive comprises an oxyamino resin which has the formula and which is prepared by quantitively reacting an epoxy resin having the formula 11, a melting point above 50 C (to ASTM E 28) and at least two ethylene oxide groups per molecule, with a secondary amine having the formula 111:

in which R, and R each denote a straight-chain alkyl group having up to four carbon atoms or together denote a lower alkylene group which can be interrupted by a heteroatom.

This reaction leads to a new class of tertiary amine, viz. oxyamino resins having the partial formula I, which are very suitable as adhesives between the substrate and the mica and also as accelerators in the curing of the epoxy resin systems added subsequently for impregnation.

The reaction must be quantitative; if it is not, the tertiary amine groups involved initiate the reaction of the ethylene oxide groups remaining in the molecule and the adhesive is unstable. The novolak kinds of epoxy resin are very suitable, as are the kinds on a base of bisphenol or heterocyclene; cycloaliphatic resins, however are less satisfactory.

Epoxy novolaks have the following basic structure:

quantity of from 1 to 3 equivalents referred to the epoxy resin. So that the resulting oxyamine can be freed readily and without damage from excess amine and from solvent, it is preferred to use as solvent ke- 5 tones or aromatic hydrocarbons or their mixtures whose boiling point is preferably below 150 C.

A glass-silk fabric or a felt of glass fibers or synthetic fibers makes a particularly good porous substrate material.

The adhesive and accelerator can be prepared e.g. as

follows:

1. 260 g of an epoxy novolak resin having an epoxy equivalent of approximately 200 and a melting point of 80 C are dissolved in the same quantity of toluene at 100 C. After cooling to about C, 280 g of diethylamine are added with vigorous agitation. After 5 hours of reflux reaction at from to C the temperature is'increased in steps and the surplus diethylamine and the toluene are removed by distillation. The resulting product is a resin having a melting point of C.

It is not necessary to use an epoxy novolak resin, and equally satisfactory results are obtained by using a his- 5 phenol resin, as will now be described.

2. 175 g of an epoxy resin on a bisphenol base, with a melting point of C and an epoxy equivalent of 555 are dissolved in g of toluene at 80 C. After cooling to 50 C, 70 g of diethylamine are added and heating with reflux is given at 60 C for 4 hours, whereafter the temperature is increased slowly to distill the surplus diethylamine and the toluene; the final residues thereof are removed in 40 reprecipitates cold. Alcohols and aqueous solvents do These are therefore chain-like phenol-formaldehydenovolaks with the phenolic hydroxyl groups substituted by glycidyl groups. Since the resulting oxyamines usually have a lower melting point than the starting resins, the starting resins used are those having a relatively high melting point. Examples of appropriate amines having straight-chain alkyl groups and of appropriate cyclic amines are dimethylamine, diethylamine, di-nproplyamine, pyrrolidine, piperidine, morpholine, thiomorpholine and so on. In the case of branched chains, of course, steric effects preclude or limit the accelerator effect. For practical reasons the reaction with diethylarnine is preferred.

Advantageously, the reaction with the amine proceeds in a solvent, the amine being introduced in a melting point of 70 C and an epoxy equivalent of 580 are dissolved in 500 g of toluene at 100 C. After cooling to 60 C, 102 g of diethylamine are added and the solution is reacted for 3 hours with reflux and without heating, whereafter a distillation top is connected and the temperature is increased slowly to C, surplus diethylamine and toluene being removed by distillation, whereafter the mixture is maintained in vacuo at the same temperature until distillation ceases.'No epoxy products can be detected in the resulting product, whose melting point is 70 C.

4. 575 g of an epoxy resin mixture on a bisphenol base and having an epoxy equivalent of 560 are dissolved in 500 g of toluene at 100 C. After cooling to approximately 60 C, 140 g of dipropylamine are added and the solution is agitated at 60 C for 3 hours, whereafter the temperature is increased slowly to 150 C and the surplus amine and the tolb. the mixture was placed in contact with a tape according to the invention and left in contactwith the tape at 50 C for 2 hours, whereafter the tape was removed and the mixture kept at 50 C. The viscosuene are removed by distillation. The reaction mix- 5 ity of the mixture was again checked at 20 C. ture is maintained in' vacuo at the same temperac. as in a p was Used which has p i ly e ture until distillation ceases. The resulting product impregnated with a 1 percent cobalt naphthenate softens at 70 C and is soluble in methylethylsolution (accelerator). After removal of the tape 7 kemmh h v f the viscosity of the mixture was determined at 20 la the thinly liquid epoxy curing agent mixtures such to as are used to impregnate finished lappings, the adhe- The e h e Show table L sive does not dissolve cold but becomes increasingly soluble above 60 C. y TABLE I The adhesive thus prepared can be used to stick mica Ex imam I ml W5 08 me Q M 20C paper to substrate. To this end, the resin is dissolved in p y ,3; a an" an appropriate solvent, e.g. a ketone or an aromatic hyor 2h. 0 24 h. 3 y drocarbon or mixtures thereof, and applied to the sub- Comm] (a) 323%; is f 8852; strate material, e.g. a thin glass cloth. The concentra- With tape tion of the solution is so adjusted in dependence upon 3 930 cps 022 cps rm cps 960 cps the particular applicator device used that approxiwith tape mately'. from 2 to 20 g of resin per square metre of sur- P y face are applied. After this treatment the glass cloth is 232i? m stuck to the mica paper in machine width. Strip cutting naphlhenale 1 machines can cut the lapping tapes from the material,- (c) 930 P P 1806 P 4065 n which is coiled into rolls or reels. The amount of resin 25 used should be the minimum necessary to provide a It may therefore be concluded h the p accord firm connection between the two layers, so that the ihg to the invention does not affect the Teeth/curing tapes can be cut and given mechanical lapping readiiy'. agent system of the experimental mixture, i.e., acceler- The smaller this quantity, the more readily subsequent ator is not dissolved out of the tape. On the other hand, impregnation of the finished lapping can be carried out. as the appreciable increase lhviseesity Shows, the since the tape, n the lapping producd' thereby molecular accelerator dissolves out of the tape prealso contain the accelqrator for the impregnating resin, treated with cobalt naphthenate. .It can also be shown the Same can be Stored in the impregnating tank with that the adhesive contained in the tape according to the out accelerator and therefore has a much longer life 'hvehtloh greatly reduces the gelhhg thhe of the Same than previously yet the impregnated cures very resin/Curing agent mixture as was used in the previous rapidly in the oven due to the action of the accelerator experiments at elevated temperathi'e, the Selling time present in the adhesive in the tapev Since the accelerabelhg determined at C and C in a thermostatt t i i lik it i t h d out d i i The term gelling time" is to be understood as denoting nation even at temperatures as high as from 50 to 60 the period between the instant of time at which the C, whereas metal salts enter the impregnating resin in 40 resin curing agent accelerator mixture Comes to the resimilar conditions and shorten its durability. action temperature in the thermostat, and the instant at The following figures will make these points clear. which the mixture ceases to flow freely and becomes a A liquid epoxy resin having an epoxy equivalent of gel. This can be checked by dipping a thin glass rod into approximately 180 ismixed with an equivalentquantity the mixture every few seconds and pulling it out. As of hexahydrophthalic acidanhydride. As freshly prelong as drops form, there is no gelling. As viscosity inpared, the viscosity of the mixture at 20 C is from 900 creases, filaments form, and when gelling occurs the t 1 P- f me s break 9... TABLE II Mixture plus adhesive Mixture plus (:om- Mixture plus coniadditive. Starting binod adhesive and bincd adhesive and from (iisilblll nllllllil Mixture plus accelerator based on accelerator based on or dibeiizylamiiia (ior 0.25% benzyldiethylaniine (min) dipropylamino (inin.) comparison) (hrs.) Mixture without dimethyl- Temperature, C. accelerator amine (min.) 0.25% 0.5% 1% 0.25% 0.5% 1% 0.25% 0.5% 1% Not measurable 60 46 2s 18 54 35 28 3 3 3 4to5hours 35 16 9 5 17% 11% 7% 2 7 2 2 As Table II shows, the accleration provided by the new adhesive is even more striking than an accelerator frequently recommended in practical use for resin/curing agent systems of the kind specified.

As tables l and II show, the resins having tertiary amine groups such as are used as adhesives ofthejapg The following experiments were made using this mixture:

a. the mixture was kept in a glass vessel at a thermo-.- 5

statically controlled temperature of 50 C and over. a period of time samples were taken and its viscosity at 20C checked.

according to the invention not only are not dissolved out of the tape by the solvent-free impregnating resin but also considerably accelerate curing by action on the impregnating resin remaining in the lapping at the temperature at which lappings are pressed in practice. On the other hand, a correspondingly devised combined adhesive accelerator based on dialkylamines having branched alkyl radicals has substantially no accelerating effect. y

The invention therefore provides a considerable technical advance:

1. The new lapping tape enables the impregnating process to be carried out without the tape having to be given further treatment for the provision of an accelerator, for the adhesive and the accelerator a the a P es"? in this ivvsm smym V.

H The adhesive used for the tape greatly accelerates the curing of the solvent-free resin used for impregnation.

3. Since the adhesive of the tape is virtually insoluble in the solvent-free impregnating resin during the impregnating time, the impregnating resins used can be slow-curing resin systems which can be stored cold substantially without change and whose viscosity rises little even at the impregnating temperature.

What we claim is:

l. A lapping tape for use in insulating electrical machinery after impregnation, comprising a porous substrate material, mica paper and an adhesive to bind the mica to the porous substrate, characterized in the use of a material which serves as a combined adhesive and a curing accelerator for a subsequently added impregnating resin, said material being an oxyamino resin having the formula:

two ethylene oxide groups per molecule-with a secondary amine having the formula:

8 in which R and R have the above meaning, said oxyamino resin being used in an amount of from 2 to 20 grams of resin per square meter of surface.

2. A tape according to claim 1, characterised in that the porous substrate is a glass silk fabric or a felt of glass or synthetic fibres.

3. A tape according to claim 1, characterised in that the oxyamino resin used as a combinedadhesive and accelerator is derived from an epoxy resin of the novolak kind or from an epoxy resin on a bisphenol or heterocyclene base.

4. A tape according to claim 1, characterised in that R and R each denote an ethyl group in the formula for the oxyamino resin.

5. A process for preparing a lapping tape for use in insulating electrical machinery after impregnation comprising a porous substrate material, mica paper and an adhesive to bind the mica to the porous substrate; characterized in the use of a material which serves as a combined adhesive and a curing accelerator for a subsequently added impregnating resin, said material being an oxyamino resin having the formula:

. by a heteroatom, the oxyamino resin being prepared by quantitative reaction of an epoxy resin having a melting point above 50 C (to ASTM E 28) and having at least two ethylene oxidegroups per molecule with a secondary amine having the formula:

in which R, and R have the above meaning, said lapping tape being prepared by dissolving the oxyamino resin in an organic solvent at a concentration which allows forthe application of approximately 2 to 20 grams of resin per square meter of surface of the porous substrate, applying the resin to the porous substrate material, sticking the so treated porous substrate nica paper and cutting the resulting material into tape or strip form.

6. A process according to claim 5 wherein the organic solvent is a ketone aromatic hydrocarbon. 

2. A tape according to claim 1, characterised in that the porous substrate is a glass silk fabric or a felt of glass or synthetic fibres.
 3. A tape according to claim 1, characterised in that the oxyamino resin used as a combined adhesive and accelerator is derived from an epoxy resin of the novolak kind or from an epoxy resin on a bisphenol or heterocyclene base.
 4. A tape according to claim 1, characterised in that R1 and R2 each denote an ethyl group in the formula for the oxyamino resin.
 5. A process for preparing a lapping tape for use in insulating electrical machinery after impregnation comprising a porous substrate material, mica paper and an adhesive to bind the mica to the porous substrate; characterized in the use of a material which serves as a combined adhesive and a curing accelerator for a subsequently added impregnating resin, said material being an oxyamino resin having the formula:
 6. A process according to claim 5 wherein the organic solvent is a ketone aromatic hydrocarbon. 